My central heating has been on reduced holiday setting for a week and my neighbour switched it on for our return. Now we're back, there's hot water but no heating from downstairs rads. (The 3 upstairs ones nearest the pump etc are prob only working/hot because of gravity?) I have an air separator which I've given a bash and it made the pump sound rough. can't do it again or it will leak at its soldered joints. I opened the big screw on pump and the spindle seems to be turning ok, [closed it again] and there's vibration on it so I think it ok. All rads checked and full of water. Expansion tank in loft was 1/2 full but now filled it up. The boiler fires as if all is well. The valve works between the CH and HW and all surrounding pipes to everything except downstairs rads are piping hot. I've tried various combinations to kickstart sytem. Apart from one rad all the rest have individual thermostats and I've tried on or off/upstairs or downstairs. There is one mega single rad in conservatory that's rarely turned on, doesn't have a thermostat and can't be bled but I'm assuming it's full. I turned it on full but didn't make a difference. Often it can cause gurgling when It's switched on after a long absence.
I'd be so grateful for any advice. Thanks